With the increased popularity in recent years of FM broadcast and Citizen Band radios, a need has arisen for a single antenna, suitable for mobile use (as on a motor vehicle) that would permit adequate AM and FM broadcast reception and both Citizen Band transmission and reception. This in turn required that the antenna be tuned to resonate at frequencies in both the FM (88.0-108.0 MHz) and CB (26.96-27.23 MHz) bands.
However, in the past the so-called multiple band antennas actually had only one natural resonant frequency. Such antennas were operated in one of two manners. Most antennas had to be separately matched and tuned for operation each time a different frequency band was selected for use, a difficult, costly, and often time consuming procedure, and one for which most users, being layman, were ill prepared. Other antennas were matched and tuned to a single supercritical frequency by the user after installation was complete. Not only was such single frequency matching and tuning extremely difficult if not impossible for the layman not having sophisticated field sensing equipment, but, even if properly accomplished, such was wholly inadequate for sufficient antenna efficiency over the widely separated AM, CB and FM frequency bands.